Writing instrument



FIG. 1 is a top plan view of a writing instrument showing my new design;

FIG. 2 is a bottom plan view;

FIG. 3 is a side elevational view, the opposite side being a mirror image thereof;

FIG. 4 is a front elevational view; and

FIG. 5 is a rear elevational view thereof. 

The ornamental design for a writing instrument, as shown and described. 